In modern computer systems, a file system stores and organizes computer files to enable a program to efficiently locate and access requested files. File systems can utilize a storage device such as a hard disk drive to provide local access to data or to utilize a network to provide access to data stored on a remote file server over the network. A file system can also be characterized as a set of abstract data types that are implemented for the storage, hierarchical organization, manipulation, navigation, access, and retrieval of data. The file system software is responsible for organizing files and directories.
Many companies and individuals with large amounts of stored data employ a file system as a data storage system. These data storage systems can be located local to the data to be backed up or at a remote site. The data storage systems can be managed by the entity controlling the data storage devices or a data storage service company. Data can be added to the storage system at any frequency and at any amount.
Blocked Based Backup (BBB) is a backup method where data is backed up as blocks. A block is a discrete set of bytes in a volume, where a volume is a logical data set stored in a data storage device or set of data storage devices. Traditional backup products use file based backup method where data is backed up as files. File based backup requires traversal of the file system which is a slow and inefficient process.
BBB uses a write tracker (WT) driver which keeps track of all the changes to blocks that occur in a volume. A BBB engine creates a bitmap which represents an array of blocks for all the clusters of the volume, where a cluster is a group of blocks. The BBB engine sets a bit representing a block or cluster as either true (1) or false (0) when a cluster is being modified. Initially, when the BBB engine is loaded by a kernel of an operating system, all bits are set as false. Similarly, all bits are set as false when a full backup of a volume is performed indicating that none of the blocks or cluster have changed since the last full backup.